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Epipubic bones are a pair of bones projecting forward from the pelvis of modern marsupials, monotremes and fossil mammals like Multituberculata, and even basal (the ancestors of , who lack them).
They were first described as early as 1698, but to date, their function(s) remain unresolved. Epipubic bones are often called marsupial bones because they support the mother's pouch in modern marsupials (" marsupium" is Latin for "pouch").
Trichosurus mimicked placentals in shifting hypaxial muscles attachment sites from the epipubic to the pelvis, losing the respiratory benefits (see below), but otherwise retains large epipubics.
In modern marsupials, the epipubic bones are often called "marsupial bones" because they support the mother's pouch (" marsupium" is Latin for "pouch"), but their presence on other groups of mammals indicates that this was not their original function, which some researchers think was to assist locomotion by supporting some of the muscles that flexion the thigh.
Placentals are the only mammal lineage that lacks epipubic bones, and this absence has been considered to be correlated to the development of the placenta itself; epipubic bones stiffen the torso, preventing the expansion necessary for prolonged pregnancy.
This however apparently did not prevent large litter sizes; Kayentatherium is now known to have given birth to litters of 38 undeveloped young, a considerably higher number than living monotremes or marsupials.
Additionally, the capacity for epipubic bones to prevent long term pregnancies has been debated in a 2022 study on , which proved that they were capable of producing young as developed as those of placentals despite their epipubics.Urton, James (25 July 2022). "New study challenges old views on what's 'primitive' in mammalian reproduction". UW News.
Function
Some writers have suggested
Occurrence
Only placentals, and possibly the early mammaliformes Megazostrodon and Erythrotherium, lack them;
See also
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